Synthetic Metals (v.157, #22-23)

Investigation of crown-containing styrylthiophene derivatives which are optically and electrochemically sensitive to the presence of metal cations by E. Lukovskaya; A. Bobylyova; O. Fedorova; Yu. Fedorov; S. Kardashev; A. Maksimov; A. Anisimov; F. Maurel; E. Marmois; G. Jonusauskas; Y. Didane; H. Brisset; F. Fages (885-893).
The analysis of complex formation of crown-containing styryl and bisstyryl thiophene derivatives with alkaline earth metal cations and the investigation of optical and electrochemical responses induced by metal cations are reported. The monostyryl derivative forms weakly fluorescent inclusion complexes with Mg2+ cations and weakly fluorescent anti-sandwich complex with Ba2+ cations. In case of bisstyryl thiophene compounds the Mg2+ complexes are fluorescent, whereas, the sandwich complex with composition (1b)2·(Ba2+)2 or (1b)2·(Ba2+)3 are weakly fluorescent. The results of the investigations showed that the crown-containing mono- and bisstyryl thiophene derivatives are optically and electrochemically sensitive to the presence of metal cations.The analysis of complex formation of crown-containing styryl and bisstyryl thiophene derivatives with alkaline earth metal cations and the investigation of optical and electrochemical responses induced by metal cations are reported.▪
Keywords: Crown ether; Thiophene; Styrylic derivative; Complex formation; Optical spectroscopy; Electron transfer; Charge transfer; Electrochemistry;

Electrochemical investigation of PEDOT films deposited via CVD for electrochromic applications by John P. Lock; Jodie L. Lutkenhaus; Nicole S. Zacharia; Sung Gap Im; Paula T. Hammond; Karen K. Gleason (894-898).
A patterned solid-state electrochromic device on an ITO-coated plastic substrate was demonstrated that incorporates poly-3,4-ethylenedioxythiophene (PEDOT) deposited via a solventless oxidative chemical vapor deposition (oCVD) technique. In this paper, we present a thin-film electrochemical and optical analysis of oCVD PEDOT. oCVD PEDOT films about 100 nm thick on ITO/glass had optical switching speeds of 13 and 8.5 s, for light-to-dark and dark-to-light transitions, respectively. The color contrast was 45% at 566 nm and is 85% stable over 150 redox cycles. An Anson plot indicates that oCVD PEDOT color transition speeds are limited by ion diffusion rates, rather than electron or hole conductivity. Dimensionless analysis predicts gains of up to in oCVD PEDOT redox switching speeds by reducing the film thickness an order of magnitude to 10 nm. oCVD is a temperature-controlled process capable of conformal conductive polymer depositions onto a range of substrates from the vapor phase. Compatible substrates include plastic, paper and fabric. Non-conductive dispersion additives are not needed with oCVD, eliminating a potential source of defect-causing corrosion. oCVD offers powerful capabilities that may overlap with key challenges for the designers and fabricators of organic thin-film electronics, including OLED lighting and displays, electrochromics, photovoltaics, and semiconductors.
Keywords: CVD; oCVD; PEDOT; Conducting Polymer; Electrochromic;

For the first time, poly(o-toludine-co-metanilic acid) (POM) layers have been deposited on mild steel (MS) substrate by galvanostatic (GS), potentiostatic (PS) and potentiodynamic (PD) methods. AC impedance of the electrodes has been analyzed. The shape and impedance parameters of galvanostatically prepared electrodes are similar to those of potentiostatically grown electrodes. The impedance spectra of potentiodynamically prepared electrode, however, are different. The redox behavior of POM copolymer has been studied using cyclicvoltammetric technique. Also, the copolymer prepared by potentiodynamic method has been characterized by UV–vis spectroscopy, Fourier Transform Infrared spectroscopy (FTIR) and Thermogravimetric analysis. It has been observed that polymerization of POM are greatly influenced by the method of preparation.
Keywords: Conducting polymer; o-Toludine; Potentiodynamic; Cyclic voltammetry; Impedance spectroscopy;

Current–voltage characteristics of an organic diode: Revisited by Pankaj Kumar; S.C. Jain; Vikram Kumar; Aparna Misra; Suresh Chand; M.N. Kamalasanan (905-909).
For over 40 years the current–voltage (JV) characteristics of an organic diode with exponentially distributed traps have been interpreted using the equation J  ∝  V m , where m  > 2. This equation is based on the classical work of Helfrich and Mark (W. Helfrich, P. Mark, Z. Phys. 168 (1962) 495). It is based on the assumption that the injection barrier is zero. However, the recent results show that in many cases the Schottky barrier is not zero and modification in this equation is necessary. We present a mathematical simulation, taking into account the effect of non-zero Schottky barrier. The experiments show good agreement with the simulated results.
Keywords: Exponential traps; Charge transport; P3HT;

Doped and de-doped polypyrrole nanowires by using a BMIMPF6 ionic liquid by Hyun Seung Kim; Dong Hyuk Park; Yong Baek Lee; Dae-Chul Kim; Hyun-Jun Kim; Jeongyong Kim; Jinsoo Joo (910-913).
We electrochemically synthesized π-conjugated polypyrrole (PPy) nanowires by using an environmentally stable and recyclable ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), as a dopant, based on an anodic alumina oxide (Al2O3) nanoporous template. The de-doped states of the PPy nanowires were obtained from doped PPy nanowires through cyclic voltammetry (CV) using a solution of the catalyst in the BMIMPF6 ionic liquid. We confirmed the de-doped states of PPy nanowires based on a decrease of the bipolaron peak of the ultraviolet and visible (UV–vis) absorbance spectra. The formation of PPy nanowires was visualized by using scanning electron microscopy and transmission electron microscopy. We studied the optical and structural properties of the doped and de-doped PPy nanowires by UV–vis absorbance and Fourier transform-infrared spectra. Our work included obtaining a laser confocal microscope Raman spectra for a single strand of the PPy nanowires.
Keywords: Polypyrrole; Nanowire; Ionic liquid; Electrochemical polymerization;

Conductive polymer-coated textiles: The role of fabric treatment by pyrrole-functionalized triethoxysilane by Matej Mičušík; Tomáš Nedelčev; Mária Omastová; Igor Krupa; Katarína Olejníková; Pavol Fedorko; Mohamed M. Chehimi (914-923).
Polypropylene (PP) and viscose (VS) textiles were modified by the in situ synthesis of a conducting polypyrrole (PPy) overlayer. To improve adhesion of the conducting layer to the textile surface, a pyrrole-functionalized silane (SP) was synthesized and bonded onto the surface before polypyrrole formation. Moreover, to introduce hydroxyl groups into the surface, PP was pretreated by grafting vinyltrimethoxysilane by means of a radiofrequency plasma discharge. The study is focused on the influence of SP on the washing fastness of a PPy layer and, consequently, on the overall conductivity of the textiles after washing. In the case of viscose, PPy was found to penetrate the substrate. A compromise was found between the influence of SP and penetration phenomenon (best conductivity after washing: wVS–0.2SP/25Py = 3 × 10−5  S/square). In the case of polypropylene the effect of pretreatment with SP is much better than for viscose, and a higher concentration of SP leads to improved fastness of the conductive layer (wmPP–0.2SP/25Py = 3 × 10−5  S/square; wmPP–1SP/25Py = 8 × 10−5  S/square), which indicates that the coating promoted by means of SP is more favoured than for viscose.
Keywords: Conductive textile; Polypyrrole; Polypropylene; Viscose; Electrical conductivity;

Synthesis and polymerization studies of 3-(+) and (−)-menthyl carboxylate pyrroles by Richard C. Foitzik; Elspeth K. Bowen; Amelia M. Taylor; Frederick M. Pfeffer; Akif Kaynak (924-929).
The synthesis of 3-(−)- and 3-(+)-menthyl carboxylate pyrrole was achieved in four high yielding steps, including the triisopropylsilyl (TIPS) protection of the pyrrole nitrogen, bromination of the 3-position, lithium halogen exchange followed by reaction with menthyl chloroformate, and finally de-protection. Chemical polymerization of both the TIPS protected, and non-protected, menthyl carboxylate pyrroles was performed and the resulting polymers exhibited conductivity ranging from 0.6 to 2.3 S/cm. Polymerization of the 3-menthyl-N-TIPS pyrrole on the surface of wool was achieved by using solution and mist polymerization methods.
Keywords: Conductive polymers; Chiral polymers; Wool; Coloured polymers; Chemical polymerization;

On the role of hydrogen in organic magnetoresistance: A study of C60 devices by T.D. Nguyen; Y. Sheng; M. Wohlgenannt; T.D. Anthopoulos (930-934).
The organic magnetoresistive (OMAR) effect has been observed in many different organic semiconductors, whereas a corresponding effect has not been reported for inorganic ones. What property makes organics behave so differently regarding magnetotransport? By studying C60 devices using several different electrode materials we show that C60, unlike many other organic semiconductors, does not exhibit any intrinsic OMAR effect. However, we find that as soon as the carriers in C60 are brought in proximity with hydrogen-containing compounds, either in the form of a polymeric electrode, or side-chain substituents, a weak OMAR effect is observed. This shows that hydrogen is crucial for the observation of OMAR.
Keywords: Organic magnetoresistance; OMAR; Hyperfine; Carbon-60; PCBM; Fullerene;

Pattern replication in polyaniline–polystyrene thin films by J. Haberko; J. Raczkowska; A. Bernasik; J. Rysz; A. Budkowski; W. Łużny (935-939).
Blends of polyaniline doped with camphorsulfonic acid (PANI(CSA)) and polystyrene (PS) were spin-cast from chloroform onto gold substrate patterned with a hydrophobic self-assembled monolayer (CH3-SAM). As a result, the replication of the substrate pattern into the formed thin films was obtained, observed as pattern-directed variation of both film thickness and polyaniline distribution. The thin films were examined by means of optical microscopy, atomic force microscopy (AFM) and secondary ion mass spectrometry (SIMS).
Keywords: Pattern replication; Polyaniline; Spin-coating; Thin polymer film;

Synthesis and characterization of triphenylamine derivatives by oxidative polymerization by Jae Ho Sim; Kohei Yamada; Sang Ho Lee; Seiji Yokokura; Hisaya Sato (940-944).
Hole transport polymers consisting of 4-methoxytriphenylamine (P-MOTPA) and 4-n-butyltriphenylamine (P-BTPA) were synthesized by oxidative coupling reaction using FeCl3 as an oxidant. These polymers had good solubility and their thin films showed sufficient morphological stability. 1H NMR and 13C NMR revealed that the monomers were exclusively connected at the p-positions of unsubstituted phenyl groups. Polymers had UV absorption maximum around 370 nm. Cyclic voltammograms of polymers showed well-defined pairs of reduction and oxidation peaks at 1.1 V versus Ag/AgCl, indicating that the polymers are electrochemically active. P-MOTPA and P-BTPA had hole drift mobility of being 4.04 × 10−5 and 2.98 × 10−5  cm2/V s at the electric field of 50 V/μm, respectively.
Keywords: Oxidative polymerization; Reduction; Oxidation; TPA(Triphenylamine);

Polyaniline (PAni) doped with organic protonic and polymeric acids shows better solubility and processability by conventional methods. In this work, we report the results of polyaniline doped with dodecylbenzenesulfonic acid (PAni-DBSA) and reprocessing with polystyrene sulfonic acid (PSS) in an internal mixer, to obtain a conductive polymer blend (PAni-DBSA/PSS).Impedance spectroscopy, scanning electron microscopy and infrared spectroscopy of the samples were evaluated. Significantly different morphologies were observed for PAni-DBSA and PAni-DBSA/PSS complexes. The effect of different degrees of doping with DBSA and the influence of PSS on the dielectric properties of PAni were investigated by impedance spectroscopy in frequency range 10 Hz–30 MHz. The different complexes present two dielectric relaxation processes suggesting two types of chain structure.We show that DBSA improves the doping range of the PAni/PSS complexes and the homogeneity of the blends.
Keywords: Polyaniline; Polystyrene sulfonic acid; Impedance spectroscopy; Dielectric relaxation;

The present article describes successful evaluation of interesting photophysical properties of multiple double bond terminated fullerene core star-like acyclic hemi-ortho esters. These hemi-ortho ester derivatives are synthesized by the selective nucleophilic addition reactions of fullerenol on to the carbonyl group of the different vinyl esters. The ground state electronic interactions are observed from the appearance of the structured absorption bands in the UV–vis spectra. Photoexcited state electronic transition from S 1 to h u and formation of charge transfer exciplex is detected from the appearance of strong emission energy peak at 1.85–1.87 eV and quenching of luminescence intensity compared to fullerenol and vinyl esters.
Keywords: Fullerene core star-like hemi-ortho ester; Photophysical properties; Charge transfer complexes; Multiply functionalized fullerene derivatives;

Enhanced efficiency of polymer:fullerene bulk-heterojunction solar cells with the insertion of thin CdS layer near the Al electrode by Yan Li; Yanbing Hou; Yan Wang; Lifang Qin; Zhihui Feng; Bin Feng; Feng Teng (956-960).
The insertion layer of cadmium sulfide (CdS) between polymer–fullerene blend and Al electrode is used to enhance the short-circuit current (I sc) and the power conversion efficiency (PCE). The solar cells based on the blend of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and C60 with the function layer of CdS (∼10 nm) shows the open-circuit voltage (V oc) of ∼0.7 V, short-circuit current (I sc) of ∼4.6 mA/cm2, filling factor (FF) of ∼0.28, and the power conversion efficiency (PCE) of ∼5.3% under monochromatic light (532 nm) photoexcitation of about 16.7 mW/cm2. Compared to cells without the CdS layer, the power conversion efficiency increases about an order of magnitude. The thickness of CdS layer was varied from 10 to 40 nm using e-beam deposition, and we obtained optimum current density–voltage characteristics for 10 nm thick CdS layer.
Keywords: Organic solar cell; Bulk-heterojunction; CdS; MEH-PPV; C60;

Micropatterning of a stretchable conductive polymer using inkjet printing and agarose stamping by Thomas Steen Hansen; Ole Hassager; Niels B. Larsen; Noel B. Clark (961-967).
A highly conducting stretchable polymer material has been patterned using additive inkjet printing and by subtractive agarose stamping of a deactivation agent (hypochlorite). The material consisted of elastomeric polyurethane combined in an interpenetrating network with a conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT). The agarose stamping produced 50 μm wide conducting lines with high spatial fidelity. The deactivation agent was found to cause some degradation of the remaining conducting lines, as revealed by a stronger increase in resistance upon straining compared to the pristine polymer material. Inkjet printing of the material was only possible if a short-chain polyurethane was used as elastomer to overcome strain hardening at the neck of the droplets produced for printing. Reproducible line widths down to 200 μm could be achieved by inkjet printing. Both methods were used to fabricate test patterns that allowed the electrical resistance parallel and perpendicular to the elongation direction to be measured. Electrical resistance increased both parallel and perpendicular to the direction of strain, with a faster increase observed parallel to the straining.
Keywords: PEDOT; Conductive polymer; Elastomer; Micropatterning; Stretchable; Inkjet; Stamping;

3,6-Di(diphenylamino)-9-alkylcarbazole-based hole-transporting hydrazones by B. Klejevskaja; E. Burbulis; A. Michaleviciute; J. Ostrauskaite; J.V. Gražulevičius; V. Jankauskas (968-973).
The synthesis of a series of new glass-forming hydrazones containing carbazole and diphenylamine moieties is reported. The thermal, optical and photoelectrical properties of mono-, di- and tetra-substituted compounds are compared. The glass transition temperatures of the newly synthesized hydrazones range from 75 to 145 °C. The ionization potentials of the films of hydrazones, measured by the electron photoemission technique, range from 4.74 to 5.15 eV. Hole-drift mobilities of the solid solutions of hydrazones in bisphenol Z polycarbonate (50 wt.%) are in the range of 6.3 × 10−6 to 1.1 × 10−5  cm2/Vs at electric field of 6.4 × 105  V/cm as characterized by the time-of-flight method.
Keywords: Low-molar-mass glasses; Hydrazones; Ionization potential; Hole-drift mobility;

Characterization of poly(N-alkylanilines) by Raman spectroscopy by Maija Blomquist; Tom Lindfors; Ari Ivaska (974-983).
Thin films of poly(N-alkylaniline) were synthesized in acidic aqueous solution and in mixtures of aqueous and organic solvents. The polymer films (alkyl = methyl, ethyl, propyl and butyl) were characterized by Raman spectroscopy with the excitation wavelengths of 514.5, 632.8 and 780 nm. The main Raman bands have been characterized for the leucoemeraldine, emeraldine and pernigraniline oxidation states between −0.2 and 0.8 V (vs. Ag|AgCl). This fundamental study shows that the structure of the half-oxidized emeraldine form contains quinoid units, which supports the commonly accepted oxidation and reduction scheme of poly(N-alkylanilines).
Keywords: Poly(N-alkylanilines); Electropolymerization; Raman and UV–vis spectroscopy; Cyclic voltammetry;

Trapping effects on the frequency response of dithiolene-based planar photodetectors by T. Agostinelli; M. Caironi; D. Natali; M. Sampietro; M. Arca; F.A. Devillanova; V. Ferrero (984-987).
The paper analyses the interrelation between the signal frequency response in an organic planar photodetector and the distribution of traps of the active material playing a fundamental role in the transport of charge carriers. In particular, the response of a dithiolene-based photodetector spectrally matched to the near infrared has been acquired under optical pulses ranging from 10 Hz to 1 MHz in frequency. By means of modulated photocurrent spectroscopy, the trap density distribution of the dithiolene in the solid state has been extracted. The capture and release of photogenerated carriers exerted by a Gaussian density of trapping states, located 0.42 eV below the transport energy, is shown to be the responsible for the observed device frequency response.
Keywords: Organic photodetectors; Trap density distribution; Modulated photocurrent;

GPC characterization of emeraldine base in NMP containing ionic liquids by Dali Yang; Andrei G. Fadeev; Phillip N. Adams; Benjamin R. Mattes (988-996).
Strong aggregation between chains of polyaniline (PANI) emeraldine base (EB) molecules dissolved/dispersed in N-methyl-2-pyrrolidinone (NMP) results in a multi-modal molecular weight distribution in gel permeation chromatograph (GPC) results, regardless of how low the concentration of EB is. The addition of a salt, such as lithium chloride (LiCl), is known to improve EB solubility in NMP by deaggregating the polymer chains. However, we have found that ionic liquids, such as 1-methyl-3-butyl imidazolium tetrafluoroborate ([BMIM][BF4]) or 1-methyl-3-ethyl imidazolium tetrafluoroborate ([EMIM][BF4]), not only have less impact on the EB chain conformation than LiCl does, but also deaggregate the EB molecules more effectively. A mono-distributed GPC peak is obtained for EB (M w up to 3 × 105  g/mol) dissolved in the NMP/ionic liquid solutions. Therefore, the EB molecular weight distribution is characterized more accurately by using the NMP/ionic liquid solution than the NMP/LiCl solution.
Keywords: Polyaniline; Emeraldine base; Aggregation; Ionic liquid; GPC; UV–vis spectroscopy; LiCl; Hydrogen bond; Molecular weight determination;

Transparent conductive thin films based on chemically assembled single-walled carbon nanotubes by Myung-Sup Jung; Tae-Lim Choi; Won-Jae Joo; Jin-Young Kim; In-Taek Han; Jong Min Kim (997-1003).
Transparent conductive thin films were fabricated by the chemical assembly of carboxylated single-walled carbon nanotubes (ca-SWNTs) onto aminosilane-modified glass plates. The ca-SWNTs were deposited with multilayer structures by amidation reaction between the carboxylic acid groups of ca-SWNTs and amino groups of linker molecules with the aid of coupling agents. Unlike the chemically assembled SWNT layers reported thus far, these SWNT assemblies have high-density structures and excellent surface adhesion due to direct chemical bonding to their substrates, which results in high electrical conductivity. The covalent bonds of the SWNT thin film were characterized by X-ray photoelectron spectroscopy, and the structures of SWNTs in the conductive thin film were analyzed by Raman spectroscopy. Imaging by scanning electron microscopy shows that the SWNT thin film has a uniform morphology with high-density multilayer structure over large areas, and UV–vis spectroscopy analysis shows that the transmittance of SWNT thin film in visible light region is excellent and further improved to greater than 90% upon thermal treatment at 250 °C. The electrical resistivities of the ca-SWNT thin film were found to be 5–10 Ω cm, which was improved to 0.2–0.4 Ω cm by the thermal treatment. The work function measured by photoelectron spectroscopy in air was found to be 5.12 eV.
Keywords: Carbon nanotubes; Chemical assembly; Transparent conductive film;

Phosphorescent organic light-emitting diodes without hole blocking layer were developed by using a charge confining device structure which can confine excitons within light-emitting layer. Narrow triplet bandgap host material was sandwiched between wide triplet bandgap host materials and excitons could be effectively confined in narrow bandgap host light-emitting layer. The charge confining devices showed excellent device performances even without hole blocking layer because excitons were confined inside light-emitting layer.
Keywords: Charge confinement; Hole blocking layer; Phosphorescent organic light emitting diodes;

A facile synthesis of polythiophene nanowires by Mohammad Rezaul Karim; Kwon Taek Lim; Chul Jae Lee; Mu Sang Lee (1008-1012).
Polythiophene nanowires have been synthesized by the gamma radiation-induced chemical oxidative polymerization method. The resultant fiber-like polymer structures were identified by the field-emission scanning electron microscopy with diameter of the order of 50–100 nm and a length of up to several millimeters. Different characterizations, e.g. elemental analysis, Fourier transform infrared, Raman spectroscopy, and X-ray photoelectron microscopy were utilized to prove that conducting polythiophene was synthesized successfully by this facile method.
Keywords: Conjugated polymers; Nanoparticles; Radiolysis polymerization; Facile synthesis;

Flexible self-assembled membrane and hollow spheres (1.7–4.6 μm in diameter) accompanied with self-assembled membrane of poly(3,4-ethylenedioxythiophene) doped with acetic acid were synthesized in aqueous solution using ammonium persulfate as oxidant. Scanning electronic microscope imagines approved the flexible membrane and sphere-like morphologies and indicated a “grow from membrane” process. The mechanism of self-assemble phenomenon was discussed by Fourier transform infrared and differential scanning calorimeter. It was found that self-assembly was driven by the hydrogen bond between 3,4-ethylenedioxythiophene monomers and acetic acid. The concentration of acetic acid plays an essential role in the self-assemble process. Moreover, the electrochemical properties of them with different morphologies were also characterized by cyclic voltammetry.
Keywords: Poly(3,4-ethylenedioxythiophene); Hollow sphere; Membrane; Self-assembly; Hydrogen bond;

Erratum to “ Fabrication of (TMTSF)2PF6 thin crystals in a confined electrode” [Synth. Met. 157 (2007) 492–496] by Yoon-Kyoung Han; Kyung-In Son; Woun Kang; Chang Seop Hong; Dong-Youn Noh (1019).